A gas fuel tank mounted on a gas fuel vehicle is filled with liquefied petroleum gas (LPG) or compressed natural gas (CNG). A hydrogen tank mounted on a fuel cell vehicle is filled with liquefied hydrogen or high-pressure hydrogen gas.
Japanese Patent Application Laid-Open No. H7-195948 (published in 1995) discloses a structure for relieving excess pressure in a gas fuel tank by discharging gas from the gas fuel lank together with vaporized fuel to the outside by use of a relief valve when an internal pressure in the gas fuel tank is increased.